1. Field of the Invention
The invention relates to a method and a device for spectral analysis in several frequency bands with different frequency resolution.
2. Description of the Related Art
To determine the spectrum of a signal within a wide frequency range using a spectrum analyser or network analyser, the frequency range to be investigated is divided into several frequency bands each with a specific frequency resolution. By contrast with a technical solution with one frequency band and one frequency resolution for the entire frequency range, this achieves a significant reduction in the computational volume for determining the spectrum to be presented in a logarithmic frequency axis and also increases the range of display options for the spectrum to be analysed.
One substantial, hitherto-unresolved problem of spectral analysis in several frequency bands with different frequency resolution is the occurrence of instabilities in the transitional range between two frequency bands. These instabilities result from extremely narrow-band spectral components of the spectrum to be measured—for example, discrete spectral lines of periodic signal components in the usable signal or discrete spectral lines of sinusoidal interference—in the transitional range between two frequency bands. If this discrete spectral line, as shown in FIG. 1, occurs at the edge of the frequency band with the relatively higher frequency resolution, this discrete spectral line is identified not only by the discrete Fourier analysis producing the spectrum in the frequency band with the relatively higher frequency resolution, but also by the discrete Fourier analysis producing the spectrum in the frequency band with the relatively lower frequency resolution.
As shown in FIG. 1, the spectrum of the discrete spectral line of the sinusoidal interference signal to be presented has already decayed because of the narrow-band window function of the discrete Fourier analysis for the frequency band with the relatively higher frequency resolution at the edge of this frequency band—empty circle of the associated spectral value—, while the discrete Fourier analysis for the frequency band with the relatively lower frequency resolution already identifies the discrete spectral line of the sinusoidal interference signal disposed outside the associated frequency band because of its broader-band window function and visualises part of the spectrum of the sinusoidal interference signal to be displayed at the edge of this frequency band—filled circle of the associated spectral value.